sysupdate: add new component "sysupdate"

src/sysupdate/sysupdate-cache.h

@@ -0,0 +1,18 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+#pragma once
+
+#include "hashmap.h"
+
+typedef struct WebCacheItem {
+        char *url;
+        bool verified;
+        size_t size;
+        uint8_t data[];
+} WebCacheItem;
+
+/* A simple in-memory cache for downloaded manifests. Very likely multiple transfers will use the same
+ * manifest URLs, hence let's make sure we only download them once within each sysupdate invocation. */
+
+int web_cache_add_item(Hashmap **cache, const char *url, bool verified, const void *data, size_t size);
+
+WebCacheItem* web_cache_get_item(Hashmap *cache, const char *url, bool verified);